Adam Griffiths drowned trying to rescue his best mate in rough surf in Hawaii and the tributes pouring in from the Australian expats in San Francisco's tech community are befitting a man of that virtue.

"Adam perfectly fit the American stereotype of an Australian - large in stature and in personality; big hearted and often smiling; irreverent; he had a real mischievous streak too," said his boss Patrick Collins, president of mobile technology company 5th Finger.

"He was technically brilliant and an awesome team member and friend for us. The last two days have been very difficult for our company as we mourn the sudden loss."

Australian technologist John Papandriopoulos, who also moved to San Francisco to further his high-tech career and was friends with Griffiths, said in a phone interview he was well-known in the Silicon Valley community.

"The thing that's resonated with everyone is that he's just a really nice guy that has always been supportive of everyone," he said. "He typifies the Australian larrikin approach, really positive about everything, everyone loves the guy and I think all those reasons are the reasons why everyone is in disbelief."

Papandriopoulos said Griffiths' final act of jumping in to save his friend Brian Baker, 47, while holidaying off Hawaii's Kauai Island, where they both perished, was "true to his character of wanting to help people out and putting everyone else first as opposed to himself".

Baker, whose body has not been found, had been knocked into the water by a large wave while they were exploring a cove. The pair has been described as "inseparable".

5th Finger, where Griffiths, 46, worked as a project manager in San Francisco, was founded in Sydney, but acquired by US firm Merkle in 2012 after relocating its headquarters to the US in 2007.

The company and Australian expat organisation Advance, where Griffiths also worked between 2009 and May last year, are holding "a large party celebrating Adam's life on Friday in San Francisco", Collins said.

Collins, a former chief technology officer of Fairfax Digital, said at 5th Finger Griffiths "helped us deliver some of the most complex client projects for very large well known brands". He was a much-loved "loud and proud Aussie team member".

His fiancee, Jennifer Kwong, who witnessed the incident in Hawaii, earlier told the San Francisco Chronicle that she was in "shock" at losing "a very lovable man" who "lights up the room wherever he goes".

Kwong had planned to wed Griffiths in September after six years together.

Papandriopoulos said, like him and other Australians in San Francisco, Griffiths went to the US after winning the green card lottery.

Another friend from 5th Finger, Christina Statescu, said Griffiths was reliable, selfless, constantly smiling and "often humming random made up songs at his desk, he always had time to stop and see humour in any situation".

Solomon Lichter said he was the most good-natured, optimistic person he has known with "an enthusiasm for life that was contagious".

"It's no surprise that he passed away from us doing something he often did in his professional life, selflessly helping someone in need."